A number of professional software tools don't make it particularly easy to visualize the internal states of the thing they're operating on.

The experts who use them are trained so they don't "need" them.

Visualization is expensive to set up, but it makes whole classes of errors immediately self-evident in a way that they aren't, even for an expert.

Fable-class models make it trivial to make visualizations, making it easier to find these error states, even for non-experts.